This invention relates to a short range, hand held, FM radar device having a unique tracking operation and a linearizing sweep for a varactor drive to a Gunn diode which generates the rf signal. The target signal is read as distance on an LED display; an audio output simultaneously produces a frequency tone proportional to target distance.
The tracking circuit which is employed by the invention also can be utilized for other purposes besides radar. This includes radio receivers, hum rejection, morse code reception, speech recognition, S/N improvement of electrocardiogram signals, lock-in amplifiers, discriminators, frequency synthesizers, etc., where it is desired to improve the S/N of a slowly moving signal.
Many needs exist for a short range radar device that is both inexpensive and lightweight. As an example, small craft such as sailboats and small powerboats could use such a radar device since these craft cannot justify the size, weight and expense of a more conventional radar system. Although effective only at short range, a lightweight, short range radar device would be highly desireable since a slowly moving craft could easily avoid a collision or an obstacle if the operator were to have sufficient warning. Even a large craft could employ a short range, portable radar; if it were moored or drifting, detection of an oncoming craft would enable the operator to adopt collision avoidance procedures.
Furthermore, if a radar device were portable, it could be utilized by the owner at various locations rather than having it confined to a fixed installation. This flexibility would increase the value of the device since it could be rented and therefore be used very frequently.
Many radar devices employ a klystron tube for the rf oscillator, and this represents an expensive component of the system; replacement of this tube by, say, an rf Gunn oscillator and tuning diode would considerably reduce the overall cost of the radar device. However, for FM modulation, it is preferable to employ a suitable wave form to the tuning diode to obtain a target signal that is linear with respect to distance.
Finally, it is important that a suitable target discriminator system is utilized which is inexpensive, effective, and can provide a fast response time for adequate signal discrimination.